.

wcfs/wcfs.go

@@ -323,9 +323,9 @@ type BigFileData struct {
 
 	bigfile *BigFile
 
-	// inflight loadings from ZBigFile
+	// inflight loadings of ZBigFile from ZODB
 	loadMu  sync.Mutex
-	loading map[int64]*blkLoadState
+	loading map[int64]*blkLoadState // #blk -> ...
 }
 
 // blkLoadState represents a ZBlk load state/result.
@@ -528,7 +528,7 @@ func (bfdata *BigFileData) readBlk(ctx context.Context, blk int64, dest []byte)
 		loading = &blkLoadState{
 			ready:   make(chan struct{}),
 		}
-		bfdata.loading = loading
+		bfdata.loading[blk] = loading
 	}
 	bfdata.loadMu.Unlock()
 
@@ -547,6 +547,8 @@ func (bfdata *BigFileData) readBlk(ctx context.Context, blk int64, dest []byte)
 	}
 
 	// noone was loading - we became reponsible to load this block
+
+	zbf := bfdata.bigfile.zbf
 	blkdata, err := zbf.LoadBlk(ctx, blk)
 	loading.blkdata = blkdata
 	loading.err = err
@@ -555,7 +557,7 @@ func (bfdata *BigFileData) readBlk(ctx context.Context, blk int64, dest []byte)
 	// data loaded with error - cleanup .loading
 	if loading.err != nil {
 		bfdata.loadMu.Lock()
-		delete bfdata.loading[blk]
+		delete(bfdata.loading, blk)
 		bfdata.loadMu.Unlock()
 		return err
 	}
@@ -574,18 +576,22 @@ func (bfdata *BigFileData) readBlk(ctx context.Context, blk int64, dest []byte)
 	// in deadlock inside kernel.
 	//
 	// .loading cleanup is done once we are finished with putting the data into OS cache.
+	// If we do it earlier - a simultaneous read covered by the same block could result
+	// into missing both kernel pagecache (if not yet updated) and empty .loading[blk],
+	// and thus would trigger DB access again.
 	go func() {
 		// XXX locking - invalidation must make sure this workers are finished.
 		st := gfsconn.FileNotifyStoreCache(bfdata.Inode(), blk*blksize, blkdata)
 
 		bfdata.loadMu.Lock()
-		delete bfdata.loading[blk]
+		delete(bfdata.loading, blk)
 		bfdata.loadMu.Unlock()
 
+		// XXX where to report error
 		if st != fuse.OK {
 			return fmt.Errorf("bigfile %s: blk %d: -> pagecache: %s", zbf.POid(), blk, st)
 		}
-	}
+	}()
 
 	return nil
 }